Urinalysis testing for the detection of tetrahydrocannabinol (THC) or its metabolites has become prevalent in the workplace. THC is an active ingredient in the illegal drug marijuana. The U.S. Armed Forces routinely screens personnel for illegal drug use, often discharging those who test positive. Many companies now screen job applicants for evidence of illegal drug use and will refuse employment to applicants with positive results. Some employers conduct random urinalysis test of their employees to identify potential drug abusers. Employees having even minimum detectable levels of a THC metabolite in their urine are frequently dismissed.
The drug testing procedures used by testing laboratories often detect very small levels of the metabolites of THC in the urine; however, there has been evidence that these test results yield an abundance of false positives. In other words, many innocent people can be dismissed or refused employment because their urine indicates small amounts of a substance which was erroneously identified as a THC metabolite.
Survey results from the Council on Marijuana and Health and the National Institute on Drug Abuse show that white and non-white people have maintained approximately equivalent marijuana-use prevalence rates. In 1971, 150 out of every 1000 persons, whether white or non-white, was reported to have used marijuana within one month prior to the survey. By 1982, the prevalence rates for white users was 4% higher than the rate for non-whites. However, when urine samples are analyzed for the presence of THC metabolites, an unexplainably higher number of non-whites test positive.
As an example of these skewed results, a group of police cadets in Cleveland, Ohio, were tested for marijuana use one month before their graduation from the police academy. Ten out of 20 Black and Hispanic cadets tested positive for marijuana use; whereas, a THC metabolite was detected in the urine samples of only three out of 20 White cadets. All of the cadets knew they were to be tested and maintained that they had not used marijuana.
These results indicate that there may be an abnormally high number of false positives associated with non-white test subjects. The present invention has indicated that the pigment melanin can be responsible for the false positive test results for marijuana use. It is undisputed that there is more melanin in the urine of dark-skinned people than in light-skinned people. Schwartze, G., Bohlke, R., Effects of Different Skin Diseases, Skin Color and Season on Indolemelanogen Content in Urine, Dermatol, Monatsschr. Vol. 161[8], pp. 617-621, 1975. Furthermore, the size and structure of melanin and THC metabolite fragments are similar. Consequently, marijuana testing procedures are unable to properly differentiate between melanin and marijuana.
There has been evidence that melanin molecules accumulate or "self-assemble" in body fluids after the fluids have been removed from the body. Changes in pH and temperature appear to cause this accumulation. Therefore, the amount of melanin detected in a urine or blood sample will increase with time, making the occurrence of false positives more likely with samples that have been stored for a longer duration. Due to the fact that there is a larger initial concentration of melanin in persons with darker skin, it is even more likely that elevated levels of accumulated melanin in stored samples from dark-skinned individuals will give rise to a greater number of false positive test results.
A solution of sodium nitroferricyanide, otherwise known as the Thormahlin reagent, has been used by clinicians to detect urinary melanin for medical diagnostic purposes, such as for detection of melanoma. Melanin is detected by observance of a color change after the addition of sodium nitroferricyanide to an aliquot of urine. If melanin is present in the sample, the mixture will change from a normal straw color to green, blue, brown or black. A green coloration indicates that low levels of melanin are present in the sample. Blue indicates the presence of slightly more melanin, and brown or black indicates such high levels of melanin that melanoma might be suspected.
Two methods of drug testing for THC metabolites are commonly used: immunoassay and gas chromatography/mass spectrometry (GC/MS). The immunoassay method provides a postiive test result when a receptor, or antibody, supposedly combines with a fragment of a THC metabolite molecule contained in the urine sample. Normally, the immunoassay test kit contains a solution of radioactively labeled receptors which are specific for a THC metabolite. When the receptor solution is combined with a urine sample containing the THC metabolite, the THC metabolite will attach to the receptor generating a positive signal. If no THC metabolites are present, no binding will occur and the result should be negative.
Endogenous substances and normal body chemicals having a molecular structure similar to THC metabolites, can be mistakenly recognized by assay receptors and GC/MS detectors as false indicators of marijuana use. For example, Comments on the Decision of the Comptroller General (regarding Solicitation No. DLA120-84-R-0774, 1985) about marijuana immunoassay testing, attributed a poor (48%) test confirmation rate (page 8) to "non-users whose body chemistry may mimic low level use (i.e., actually false positives)". In addition, the National Institute on Drug Abuse has observed that some endogenous compounds have been noted to have the same GC/MS test characteristics as controlled substances, Research Monograph, 32, pp. 22-23. Melanin is but one such body chemical that can mimic THC metabolites in the urinalysis testing of non-users.
The GC/MS method for determining the presence of THC metabolites in urine involves the use of an analytical instrument known as a gas chromatograph coupled with a mass spectrometer. The gas chromatograph separates many of the components present in urine. One by one, each component is introduced into the mass spectrometer where it is bombarded with electrons causing fragmentation into ions. If the component is a THC metabolite, it will be broken down into many ions including ions having mass to charge ratios (m/z) of 372, 357 and 313. Often a known amount of an internal standard such as a deuterated THC metabolite is added to each urine sample for purposes of quantitation. The deuterated metabolite is fragmented into ions having m/z of 375, 360 and 316. A GC/MS spectrum of all the ions in the sample can be compared to a standard spectrum for the THC metabolite and its deuterated metabolite to determine whether the sample contains the THC metabolite.
There are differences of opinion among researchers as to how many ion-points of comparison, found in the GC/MS spectrum, are needed to confirm the presence of marijuana metabolites. A full-scan GC/MS spectrum (a 100% spectrum comparison) contains 23 major ion-points and numerous minor ion-points for comparison in the urinalysis testing process. A spokesman for Hewlett-Packard, a leading U.S. manufacturer of the widely used GC/MS testing equipment, reportedly recommended that for detecting a controlled substance, 83% of the major ion-points, comprising a partial GC/MS spectrum, are needed (see Analytical Chemistry, Volume 51, No. 8, p.818-A, 1979). For marijuana testing, 19 of the 23 major ion-points in the THC metabolite GC/MS spectrum would meet manufacturer's 83% spectrum match specifications. In contrast, a professor from the University of California, testifying in a military court martial, expressed the opinion that 9 ion-points of comparison (39% match) should be used for marijuana testing. U.S. v. Lasley, SPS, 244-98-1754. Still another opinion by the United States chief of drug testing research technology recommends "at least four points of comparison" (Substance Abuse Report, Volume 17, No. 4,p.7, 1986). Four points would constitute only a 17% spectrum comparison leaving reasonable doubt about the accuracy of the test result.
Various drug testing laboratories, offering economical urinalyses for employment and court related purposes, routinely rely on fewer than four ion-points in their GC/MS confirmation tests for marijuana. Numerous court cases are already on record wherein the drug testing laboratory gained a conviction based on detecting merely one point (4% match) in the marijuana GC/MS fingerprint comparison step.
Laboratories generating four or more points generally proceed with a computer assisted ratio-match step; however, the computers generally allow a wide plus-or-minus variance in the matching process. A laboratory employing merely three points and allowing a maximum variance in the ratio match step cannot possibly guarantee that the substance is marijuana.
The GC/MS technique is very sensitive and can detect very small levels of a THC metabolite in the urine, even as low as 1 to 5 ng/ml. A false positive test result can therefore occur with the GC/MS technique if another urine component fragments into the same ions as the THC metabolite molecule. Due to the extreme sensitivity of the GC/MS technique, it is possible that low levels of a naturally occurring substance, such as melanin, might give rise to false positive test results for marijuana. Persons having darker skin would therefore be more susceptible to receiving false positive test results because they have higher levels of melanin in their urine.
Therefore, there is a need for a urine test that does not yield racially biased results due to structural similarities between THC and melanin.